Re: dummy net iface?

Let me clarify
If you enable ip_forward in sysctl then you can port forward from one
port to another on a dummy interface or to a port on another
interface.
Though that's unusual behavior, normally you would want to bind a
service to the dummy interface and port forward or route from a
physical interface to the dummy the service on the dummy interface so
if the physical interface goes down the service will keep listening
and traffic will resume after the physical interface is brought back
up without needing to restart the service.
However if you want to port forward on a non-routable interface to
prevent external network traffic from being able to connect to the
service then you would use a loopback interface instead because any IP
address assigned to a loopback interface becomes non-routable by
default. but note for port forwarding ip_forward will need to be
enabled in sysctl regardless if you want to forward from one port to
another. Also note you can't forward from a physical or dummy
interface to a loopback interface or vica versa.

On Fri, Feb 20, 2026 at 6:39 AM Paul Robert Marino <[email protected]> wrote:
>
> Did you enable ip_forward in sysctl ?
>
> On Fri, Feb 20, 2026 at 6:09 AM listy <[email protected]> wrote:
> >
> > Hi guys.
> >
> > 'dummy' network interface - I get that those are meant to be
> > kind of a sing/black-hole but... should such iface not
> > port-forward on itself? (as oppose to other ifaces, which it
> > does not I think)
> > So, I cannot get "normal" port-forward - firewalld with
> > nftables as per default in Fedora, which I try to do it with
> > - because it needs more tweaking for "dummy" ifaces _do_
> > port-forwarding or.. they do _not_ - do you know?
> >
> > many thanks, L.
> >